Sex And The Single Worm

A UM biologist is hoping to solve genetic mysteries of sexual development by studying females that can reproduce on their own

April 21, 2006|By DENNIS O'BRIEN | DENNIS O'BRIEN,SUN REPORTER

Eric Haag keeps millions of worms chilled in incubators at his University of Maryland lab - and watches them have sex.

As an evolutionary developmental biologist, Haag studies the tiny animal known as Caenorhabditis elegans, hoping that he can unravel some of the mysteries about the role that genes play in sexual development, how sex evolved and why we bother with it.

He knows his line of work sounds a bit weird. That's why, shortly after he began teaching biology at the College Park campus in 2002, he hung a sign outside his lab that reads: "The Palace of Worm Sex."

"You've got to have a sense of humor," he says.

Haag's research is focused on comparing Caenorhabditis elegans with Caenorhabditis briggsae, two species of worm that developed a useful reproductive trick before they went their separate ways on the evolutionary tree millions of years ago.

They evolved into hermaphrodites, essentially becoming modified females that can make sperm and use it to fertilize their own eggs. They do, however, keep some males around for evolutionary emergencies.

That conduct is common fodder for jokes among the worm's aficionados. "Women have said to me, `So - there's no dating? That's great.' I guess it's irresistible to make those kinds of comparisons," Haag said. "You can go nuts with that kind of anthropomorphism." Haag, 38, is a charter member of

the Maryland Worm Club, a loose collection of about 10 area scientists who meet every two weeks to discuss their research or the latest findings involving C. elegans.

"He's got some very good ideas," said Geraldine Seydoux, a geneticist at the Johns Hopkins University School of Medicine and a club member.

In 1998, C. elegans became the first multicellular organism to have its genome sequenced. The worm grows from birth to motherhood in four days, lives for two weeks, is easy to store, cheap to feed and maybe best of all, has transparent skin.

"You can literally see the moment of fertilization," said Robin Cook Hill, a doctoral candidate in Haag's lab who has spent hours studying C. elegans through a microscope.

Genetic puzzle

These days, Haag is trying to find the genetic mechanisms that C. elegans and C. briggsae used to evolve into hermaphrodites, why they did it in the first place, and why some of their genes, while identical, play different roles. He also is trying to pinpoint the genes that are master regulators - turning other genes off and on.

"What we've been trying to do is identify different features, different mutations in this animal and then follow the effects of those mutations across generations," Hill said.

The worms look the same and evolved from a common ancestor that reproduced with male-female sex. But genetically they are separated by what some experts believe is about 50 million years of evolution - a much wider time gap than the estimated 5 million to 8 million years that separate us from the common ancestor we share with the great apes.

At least part of Haag's work is aimed at addressing a question that perplexes some biologists: why did sex evolve in the first place?

"That's been called the queen of all problems in biological sciences," said Robert Vrijenhoek, a researcher at the Monterey Bay Aquarium Research Institute.

The one-celled organisms that dominated the planet millions of years ago never had sex. But these days, almost every other creature joins in the male-female reproductive cycle.

Sexual reproduction allows nature to select the most useful traits from each generation, minimize defective genes that could be passed on by inbreeding and create a variety of healthy progeny equipped to deal with changing environments. But it also consumes an inordinate amount of an organism's time, energy and attention.

Being able to switch from that sex thing to hermaphroditic, asexual reproduction has its advantages, biologists say. Hermaphrodites and asexual creatures don't have to bother with finding a suitable mate and so may be better equipped for static habitats, multiplying without the need for males. They also don't have to drag along males when they colonize new environments.

"I almost hate to say it, but as males, we're dispensable under many circumstances. We're just a convenience, a way to move a gene from one family to another," said David Pilgrim, a genetics professor at the University of Alberta in Canada.

A tiny percentage of the world's animals - an estimated 0.1 percent - can survive and reproduce without sex. Along with hermaphroditic worms, some fish and insects are known to switch from sexual to asexual reproduction.

"If you look at the animal kingdom, asexuality is rare, but it does exist," said Vrijenhoek, who has studied a freshwater minnow species that moves from sexual to asexual reproduction.